Vacuum-type circuit interrupter with weld-resistant contact material consisting essentially of copper and beryllium

ABSTRACT

Discloses a vacuum-type circuit interrupter having a pair of contacts relatively movable into and out of engagement with each other. The contacts have their circuit-making and breaking regions formed of an alloy consisting essentially of copper and beryllium, the beryllium being present in a quantity of about 6 to 19 percent by weight of the alloy. The alloy is substantially free of additional metallic constituents that are substantially insoluble in the solid state in copper and beryllium and have effective freezing points lower than 860* C.

United States Patent [72] Inventor Fordyce H. Horn, deceased late ofSchenectady, N.Y. by Helen W. Horn, executrlx 888,398

Appl. No.

Attorneys-J. Wesley Haubner, William Freedman, Frank L.

Neuhauser, Oscar B. Waddell and Joseph B. Forman The portion of the termof the patent b H Flt-241987h bee o e as n ABSTRACT: Discloses avacuum-type circuit interrupter having a pair of contacts relativelymovable into and out of engagement with each other. The contacts havetheir circuitmaking and breaking regions formed of an allo sentially ofcopper and beryllium, the berylliu in a quantity of about 6 to 19percent b y consisting esm being present WELD-RESISTANT CONTACT MATERIALCONSISTING ESSENTIALLY OF COPPER AND y weight of the alloy. BERYLLIUMditional metallic constituents that are substantially insoluble in thesolid state in copper and beryllium and have effective freezin than 860C.

The alloy is substantially free of ad 6 Claims, 2 Drawing Figs.

g points lower C2 4 34 m m Z M m mh "c u "M m m I L0 W d s Q U Mn. N W 555 VACUUM-TYPE CIRCUIT INTERRUPTER WITI-I WELD- RESISTANT CONTACTMATERIAL CONSISTING ESSEN'IIALLY OF COPPER AND BERYLLIUM BACKGROUND OFTHE INVENTION This application is related to my copending applicationSer. No. 562,141, filed July 1, 1966, and assigned to the assignee ofthe present invention, now US. Pat. No. 3,497,755.

This invention relates to a vacuum-type circuit interrupter and, moreparticularly, to contact structure for such an inter rupter.

The aforesaid application discloses and claims vacuum-gap electricdischarge devices having arc electrodes made of a copper-beryllium alloycontaining 0.1 to l 1.5 percent beryllium by weight. The purpose of theberyllium in such alloy is to serve as a getter that reacts with anyoxygen present in the alloy, both during processing and during operationof the discharge device, to maintain the device essentially free ofevolved oxygen during the crucial stages of its operation. The presentapplication is also concerned with a discharge device that hasarc-electrodes containing beryllium. But in the electrodes of thepresent application, the beryllium acts not only as a getter but as anantiweld agent, as will soon be described.

If the vacuum discharge device is a vacuum interrupter with electrodes,or contacts, movable into and out of engagement with each other,animportant requirement that must be met is that the contacts must notweld together with objectionable welds, even under the most severeoperating conditions. In meeting this requirement, it is important toprevent the formation not only to those welds that are so strong thatthey cannot be broken except with excessive force during a subsequentopening operation but also those welds that cannot be fractured cleanlyand without production of a jagged interface between the two contacts.The production of such a jagged interface leads to excessive contactwear and also to reduced dielectric strength. This antiweld requirementis especially difficult to meet in a vacuum-type circuit interrupterbecause the contacts of such interrupters must be extremely clean andhave surfaces devoid of contaminating films. These clean surfaceconditions are ideal for the production of objectionable welds, which,in many cases, would be largely avoided if contaminating films werepresent at the interface.

One way of meeting the aforesaid antiweld requirement is to form thecontacts of one of the alloys disclosed and claimed in US. Pat. No.3,246,979-Lafferty et al., assigned to the assignee of the presentinvention. Each of these alloys consists essentially of a majorconstituent which is a good-conductivity, nonrefractory metal and aminor constituent which is a metal having a lower freezing temperaturethan the major con stituent and little or no solid-state solubility inthe major constituent, the minor constituent being present in a quantityof a few per cent or less by weight of the alloy. Examples of suchalloys are copper-bismuth, copper-lead, silver-bismuth, and silver-lead,each alloy containing a few per cent or less by weight of thesecond-mentioned or minor constituent. The main purpose of the minorconstituent is to act as a weld-inhibiting agent that weakens any weldformed between the contacts.

While this approach is satisfactory for many vacuum interrupterapplications, there are certain applications where it appears desirableto avoid the use of the low-freezing point, relatively volatile,insoluble minor constituent. The presence of this minor constituent inthe contacts, in some cases, lirriits the manner in which the contactscan be processed and may interfere with realizing the maximum currentand voltage interrupting performance obtainable from certain contactmaterials.

SUMMARY Accordingly, an object of this invention is to provide a vacuuminterrupter that has contacts capable of meeting the above-describedantiweld requirement and yet are free of the low-freezing point,relatively volatile, insoluble minor constituents of the aforesaidLafferty et al. patent.

Another object is to provide the vacuum interrupter with contacts thatcontain beryllium to act as an effective getter of oxygen, as describedin my aforesaid application, and that are also capable of meeting theobject set forth in the immediately preceding paragraph.

In carrying out the invention in one form, the vacuum interrupter isprovided with contacts relatively movable into and out of engagement andhaving their circuit-making and cricuit breaking regions made of analloy consisting essentially of copper and beryllium, the berylliumbeing present in a quantity of between about 6 and 19 per cent by weightof the alloy. The alloy is substantially free of additional metallicconstituents that are insoluble in the solid state in copper orberyllium and have effective freezing points lower than that of thecopper-beryllium eutectic (i.e., 860 C).

BRIEF DESCRIPTION OF DRAWINGS For a better understanding of theinvention, reference may be had to the following description taken inconjunction with the accompanying drawings, wherein:

FIG. 1 is a sectional view of a vacuum-type circuit interrupterembodying one form of the invention.

FIG. 2 is an enlarged perspective view of one of the contacts of theinterrupter of FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENT Refen'ing now to the interrupter ofFIG. I, there is shown a highly evacuated envelope 10 comprising acasing 11 of a suitable insulating material, such as glass, and a pairof metallic end caps 12 and 13, closing off the ends of the casing.Suitable seals 14 are provided between the end caps and the casing torender the envelope l0 vacuum-tight. The normal pressure within theenvelope 10 under static conditions is lower than 10 mm. of mercury sothat a reasonable assurance is bad that the mean free path for electronswill be longer than the potential breakdown paths in the envelope.

The internal insulating surfaces of casing 11 are protected from thecondensation of arc-generated metal vapors thereon by means of a tubularmetallic shield 15 suitably supported on the casing 11 and preferablyisolated from both end caps 12 and 13. This shield acts in a well-knownmanner to intercept arcgenerated metallic vapors before they can reachthe casing 11.

Located within the envelope 10 is a pair of separable contacts l7 and18, shown in their engaged or closed-circuit position. The upper contact17 is a stationary contact suitably attached to a conductive rod 170,which at its upper end is united to the upper end cap 12. The lowercontact 18 is a movable contact joined to a conductive operating rod 180which is suitably mounted for vertical movement. Downward motion of thecontact 18 separates the contacts and opens the interrupter, whereasreturn movement of contact 18 reengages the contacts and thus closes theinterrupter. A typical gap length when the contacts are fully open isabout one-half inch. The operating rod 18a projects through an openingin the lower end cap 13, and a flexible metallic bellows 20 provides aseal about the rod 18a to allow for vertical movement of the rod withoutimpairing the vacuum inside the envelope 10. As shown in FIG. 1, thebellows 20 is secured in sealed relationship at its respective oppositeends to the operating rod 180 and the lower end cap 13.

All of the internal parts of the interrupter are substantially free ofsurface contaminants. These clean surfaces are obtained by suitablyprocessing the interrupter, as by baking it out during its evacuation. Atypical bakeout temperature is 400 C. In addition, the contacts 17 and18 are effectively freed of gases absorbed internally of the contactbody so as to preclude evolution of these gases during high currentarcing. The manner in which these internal gases are removed will bereferred to in more detail hereinafter.

Although my invention is not limited to any particular contactconfiguration, I prefer to use the contact configuration disclosed andclaimed in US Pat. No. 2,949,520, Schneider,

assigned to the assignee of the present invention. Accordingly, eachcontact is of a disk shape and has one of its major surfaces facing theother contact. The central region of each contact is formed with arecess 29 in this major surface and an annular circuit-making andcircuit breaking area 30 surrounds this recess. These annularcircuit-making and breaking areas 30 abut against each other when thecontacts are in their closed position of FIG. 1, and are of such adiameter that the current flowing through the closed contacts follows aloopshaped path L, as is indicated by the dotted lines of FIG. 1.Current flowing through this loop-shaped path has a magnetic effectwhich acts in a known manner to lengthen the loop. As a result, when thecontacts are separated to form an are between the areas 30, the magneticeffect of the current flowing through the path L will impel the arcradially outward.

As the arc terminals move toward the outer periphery of the disks l7 and18, the arc is subjected to a circumferentially acting magnetic forcethat tends to cause the arc to move circumferentially about the centralaxes of the disks. This circumferentially acting magnetic force ispreferably produced by a series of slots 32 provided in the disks andextending from the outer periphery of the disks radially inward bygenerally spiral paths, as is shown in FIG. 2. These slots 32 correspondto similarly designated slots in the aforementioned Schneider patent andthus, force the current flowing to or from an arc terminal located atsubstantially any angular point on the outer peripheral region of thedisk to follow a path that has a net component extending generallytangentially with respect to the periphery in the vicinity of the arc.This tangential configuration of the current path results in thedevelopment of a net tangential force component, which tends to drivethe arc in a circumferential direction about the contacts. In certaincases, the arc may divide into a series of parallel arcs, and theseparallel arcs move rapidly about the contact surface in a manner similarto that described hereinabove.

As described in the introductory portion of this application, an objectof this invention is to provide contacts capable of meeting severeantiweld requirements and yet free of the lowfreezing point, relativelyvolatile, insoluble secondary constituents of the aforesaid Lafferty etal. patent. l find that these requirements can be met by forming thecircuit-making and circuit breaking portions 30 of the vacuuminterrupter contacts of an alloy consisting essentially of copper andberyllium, the beryllium being present in a quantity of between about 6and 19 percent by weight of the alloy. The alloy is free of additionalmetallic constituents that are insoluble in the solid state in copperand beryllium, and have freezing points lower than that of thecopper-beryllium eutectic, which is 860 C. A specific alloy which hasshown exceptional ability to meet these requirements is acopper-beryllium alloy consisting essentially of copper and beryllium,the beryllium being present in a quantity of 7 percent by weight of thealloy.

When the quantity of beryllium is increased beyond about l 1.5 weightpercent, some of the intermetallic compound phase Be Cu is formed. Theintermetallic compound is very brittle material, and its presenceincreases the brittleness of the overall contact material. It appears,however, that about 19 percent beryllium can be added to copper beforeexcessive brittleness occurs. Despite the presence of the intermetallicphase when beryllium is present in amounts between I 1.5 and 19 percent,there appears to be a sufficient amount of the B phase remaining toadequately offset the brittleness of the intermetallic compound phase.Amounts of beryllium greater than about 19 percent impart so muchbrittleness that is becomes impractical to machine the material intocontacts or to subject them to closing impacts without risking cracking.

Contacts of copper beryllium containing beryllium in the range between 6and 19 percent have shown an exceptional resistance to cold welding,i.e., welding together under the influence of high pressure forcing thecontacts together with no arcing between the contacts. For example, aseries of tests have been made in which clean contacts of differentmaterials have been forced together with 3000 pounds of force, and

then separated to fracture any weld present between them. The forcerequired to separate them is measured. With contacts of thecopper-bismuth Cu-Bi (0.5% Bi) referred to in the aforesaid Lafferty etal. patent, welds requiring approximately pounds of force for theirfracture were developed. (This copper-bismuth material is believed to bethe best of the contact materials disclosed in the Lafferty et al.patent.) No cold welds were formed with contacts of the followingmaterials Cu-Be (5% Be); Cu-Be (7% Be); Cu-Be (12% Be); Cu-Be 15% Be).This freedom from substantial cold-welding is a significant advantagenot only because it reduces the force necessary to separate the contactsbut also because it reduces the likelihood that protuberances will beformed at the fractured weld which could impair the dielectric strength.

Another condition that can lead to contact-welding is that accompanyingclosing the circuit interrupter against heave currents. When thecontacts are driven into closed position, they often bounce apart ashort distance immediately after initial impact and then rebound towardeach other, aided by the closing force applied to the movable contact.An arc is drawn when the contacts first bounce apart, and this are meltsadjacent surface portions of the contacts so that when they reengage, amolten film is present at the interface. When arcing ceases followingreengagement, the energy input into the contact interface drops sharply,and the film at the interface thus quickly cools to a solid state. Theresult is the formation of a weld between the two contacts. The higherthe arcing current, the larger the surface area that will be covered bythe molten film and hence the larger and stronger the weld ordinarilywill be. The welds formed under these conditions will be referred to ashot welds.

For determining the relative strengths of welds that are formed underthese conditions, clean contacts of various materials were driventogether under high current arcing conditions, and the force requiredfor their subsequent separation was measured. To prevent the formationof oxide or other films on the contacts, these tests were run in aninert atmosphere of argon, which provides ambient conditions withrespect to oxidation closely simulating those present under high vacuumconditions. With contacts of plain copper, an opening force of 5000pounds was typically required to fracture the weld and separate thecontacts; with contacts of Cu-Bi (0.5% Bi), an opening force of -200pounds was typically required.

With contacts of copper-beryllium (3 percent beryllium) containing 1percent bismuth to reduce the weld strength, welds requiring an openingforce of over 2000 pounds for their fracture were developed. Withcontacts of copper-beryllium (5 percent beryllium), welds requiring anopening force of over 3800 pounds for their fracture were developed.

But when the amount of beryllium in the copper-beryllium alloy wasincreased to about 7 percent by weight, only about 25 to pounds ofopening force was typically required. With copper-beryllium containingabout 12% Be by weight, substantially no welds were formed. Withcopper-beryllium containing [5% Be by weight, welds requiring as much as500 pounds were developed. It appears from the above tests that when thepercentage of beryllium in the copper-beryllium alloy exceeds about 6%Be by weight, any welds developed can typically be fractured by anopening force of less than 1000 pounds, and this is acceptable for mostpower circuit breaker applications. The excessive brittleness whichresults from increasing the beryllium content above about 19 percent byweight determines the upper limit of the beryllium content.

The above-described high resistance to the formation of both hot andcold welds is an unexpected property of the contacts of copper-berylliumhaving a beryllium content in the range of 6 to 19 percent by weight ofthe copper-beryllium. The extreme weakness of the welds formed when theberylliurn content is the range of about 7 to 13 percent by weight ofthe Cu-Be is especially noteworthy.

Although there is not a large difference in the forces required forfracturing welds between the above-described copper-beryllium contacts(with 6 to 19% Be) as compared to the forces required for thecopper-bismuth contacts, it is most significant that the high weldresistance of the copper-beryllium material has been obtained withoutthe need for any bismuth or other low-freezing point,high-vapor-pressure weld-inhibiting constituent which is insoluble inthe other constituents. This is highly advantageous because the presenceof these low-freezing point, insoluble constituents in the materi als ofthe Lafferty et al. patent limits the type of surface cleaning which canbe employed in making the interrupter, imposes limitations on wherevacuum-tight brazed joints can be located, and requires an extra step inadding the insoluble constituent. Tests made with the bismuth-freecopper-beryllium alloys of my invention have also shown that increasedcurrent and voltage interrupting ability can be obtained as compared tothat obtainable with copper-beryllium contacts containing bismuth, evenin small quantities such as one percent by weight of the total alloy.

in referring to additional constituents that are substantially insolublein copper and beryllium in the solid state, I am referring to additionalconstituents that have a solid-state solubility in copper and berylliumof less than about two per cent by weight of the alloy considered at thefreezing temperature of said additional constituent. Bismuth and otherweld-inhibiting metals mentioned in the aforesaid Lafferty et al. patentare examples of such additional constituents.

In preparing these contact materials, each separate constituent firstshould be suitably processed to free it of sorbed gases and othercontaminants, as, for example, by the zonerefining process described inUS. Pat. No. 3,234,35l-l-lebb, assigned to the assignee of the presentinvention. The constituents are then melted and appropriately mixedtogether while they are in the liquid state, after which the temperatureis lowered to cause the constituents to solidify and form the solidalloy.

While I have shown and described a particular embodiment of theinvention, it will be obvious to those skilled in the art that variouschanges and modifications may be made without departing from theinvention in its broader aspects; and I, therefore, intend herein tocover all such changes and modifications as fall within the true spiritand scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is: 1

l. A vacuum-type electric circuit interrupter comprising:

a. an envelope evacuated to a pressure of 10 mm. of mercury or less,

b. a pair of highly weld-resistant contacts within said enveloperelatively movable into and out of engagement,

c. said contacts being substantially free of sorbed gases andcontaminants,

d. said contacts having circuit-making and breaking regions formed of analloy consisting essentially of copper and beryllium,

e. the beryllium being present in a quantity of between about 6 and 19percent by weight of the copper-beryllium alloy,

f. said alloy being substantially free of additional metallicconstituents that are substantially insoluble in the solid state incopper and beryllium and have effective freezing points lower then 860C.

2. The vacuum-type circuit interrupter of claim 1 in which saidberyllium is present in a quantity of about 7 to 13 percent by weight ofthe copper-beryllium alloy.

3. The vacuum-type circuit interrupter of claim 1 in which saidberyllium is present in a quantity of 6 to 19 percent by weight of thecopper-beryllium alloy.

4. The vacuum-type circuit interrupter of claim 1 in which said contactsare characterized by such a high resistance to hot welds that any hotwelds developed therebetween can be fractured by an opening force ofless than 1,000 pounds applied to one of said contacts.

5. The vacuum-type circuit interrupter of claim 2 in which said contactsare characterized b such a hi h resistance to hot welds that any hotwelds deve oped there etween can be fractured by an opening force ofless than 1000 pounds applied to one of said contacts.-

6. The vacuum-type circuit interrupter of claim 3 in which said contactsare characterized by such a high resistance to hot welds that any hotwelds developed therebetween can be fractured by an opening force ofless than 1000 pounds applied to one of said contacts.

l 0 k F

2. The vacuum-type circuit interrupter of claim 1 in which saidberyllium is present in a quantity of about 7 to 13 percent by weight ofthe copper-beryllium alloy.
 3. The vacuum-type circuit interrupter ofclaim 1 in which said beryllium is present in a quantity of 6 to 19percent by weight of the copper-beryllium alloy.
 4. The vacuum-typecircuit interrupter of claim 1 in which said contacts are characterizedby such a high resistance to hot welds that any hot welds developedtherebetween can be fractured by an opening force of less than 1,000pounds applied to one of said contacts.
 5. The vacuum-type circuitinterrupter of claim 2 in which said contacts are characterized by sucha high resistance to hot welds that any hot welds developed therebetweencan be fractured by an opening force of less than 1000 pounds applied toone of said contacts.
 6. The vacuum-type circuit interrupter of claim 3in which said contacts are characterized by such a high resistance tohot welds that any hot welds developed therebetween can be fractured byan opening force of less than 1000 pounds applied to one of saidcontacts.